Radiators KEEP needing bleeding

[Min]

Hi guys
Two radiators on first floor keep needing bleeding.

I have a pumped system which used to work fine. In August I had the back boiler removed (so I could have an open fire) and new Potterton fitted. Pipework remained the same except for last metre to new boiler.

At the same time one under-specced radiator was replaced with a new double panel one and a TRV fitted. This rad works fine though I did find a wet patch on the carpet this morning. It seems there's a small leak out of the joint for the TRV. Zone valve packed up with new boiler so that was replaced too.

Have checked all the other rads - none leaking, all heating up fine.

The boiler overspill tank has 4" water in it, ball valve working, system feed outlet (or whatever you call it) seems not to be blocked (stuck my finger down it).

Any idea what's causing the air in the rads? I bleed them and then about a week later they need bleeding again.

Thank you!

 

[Min]

I looked for a system air vent on the pipework near the bolier and couldn't find anything that looked like a likely candidate. There are two thingies, one either side of the pump (look a bit like tap spindles poking out). Not sure what they are or do.

I really couldn't work out the flow of the system - is it possible that it is gravity fed and pump assisted? The pump seems to be on the feed from the expansion tank, just below a little joining pipe to the expansion pipe (sort of forming an 'H' shape). Ignore this paragraph if it is complete rollocks!

Thanks again, Min

 

[ChrisR]

Well done for doing your homework and telling us all you can!

The spindle things are taps for isolating the pump so it can be changed without draining down.

The H configuration is exactly what it's called and it works pretty well.

4" is correct.

If the gas coming out is hydrogen then it's from corrosion so add inhibitor. Test gas using upturned tumbler and a cig lighter - it goes pop.

COuld also get a jar with some system water in it with a clean nail - see if it rusts over a couple of weeks. What colour is the water?

Could be you are taking air in from a micro leak on the input side of the pump. Check everything is tight. Any signs of leaks there will do it.

SOme systems seem to take a long time to vent fully - a few weeks. Unless its from acid flux left in the system, I don't really know why. Maybe someone olderanwiser will make suggestions!

 

[Min]

When I bleed the radiaotors the water is blackish and gas has that iron/metally smell.

Does the H config mean it is pump-assisted gravity fed system?

I will try hydrogen test (I remember my school chemistry lessons) but I do believe Fernox was added when system refilled with new boiler.

On the pump isolating valves (taps?) there is evidence of leakage in that there's hard water type deposit from them, and from the upper one, it's run down all over the pump. But it wasn't wet when I checked this morning. Frustrating thing is that I don't know if that was there before all the work commenced.... I'll keep checking for the next few days while the system is hot and cold.

I will check tightness of pump connection (any excuse to get my Stilsons out).

Best of all I like suggestion that it takes a systema few weeks to vent. It's just that August to December seems like a long time. Though I suppose the heating didn't come on til late Sept. I will keep bleeding and let you know.
Many thanks Chris
Min